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Author Topic: RPM / Feed Rates Again?  (Read 983 times)

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Offline kolias

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RPM / Feed Rates Again?
« on: March 12, 2017, 10:47:39 PM »
Searching on this subject I find a lot of answers but not what I’m looking for

For example I found this formula: ChipLoad x CutterDiameter x Number of Flutes x SpindleRPM = FeedRate in Inches/min.

Perhaps I’m wrong but the above formula does not take into the account how much material we hog per pass. Is the above formula correct regardless the depth of cut?

I was hoping to find a table summarizing most materials but I didn’t find any

I’m working on MDF and I found the ChipLoad for MDF is 0.1 to 0.18. Using 0.18 to the formula above with 1/8” Single Flute at 18000RPM gives me a feed rate of 405 inches/min. I wouldn’t even dream to use this kind of feed rate so either I do something wrong or the formula is not applicable for MDF material.

Anyone knows what the feed rate will be if I use 1/8” Single flute on MDF? (my spindle can go from 6000 – 24000 RPM and normally I take 1/16 to 1/32 per pass).
Nicolas

Offline Davek0974

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Re: RPM / Feed Rates Again?
« Reply #1 on: March 13, 2017, 03:29:35 AM »
I would go get a demo copy of HSMAdvisor - it takes into account tool flex, torque and much more, i use it all time and its been good so far:)

No connection, just a happy user.
Bridgeport Mill, Mach3 V062, CSMIO-IP/A controller, AC Servo Drives
Re: RPM / Feed Rates Again?
« Reply #2 on: March 13, 2017, 05:57:09 AM »
Hi,
I go with Dave, HSMAdvisor is good, so much so I bought it!

Don't know whether its much cop on non-metals.

The calculation really comes down to chipload. I use very small endmills (0.4-0.5mm) for circuit boards and I allow 1% diameter per flute per rev.
This keeps the cutting forces mid to low when the cut depth is 50% of diameter. For larger endmills say 3-6mm I go to 2% per flute per rev and
decent size ones say 12-16mm 3% per flute per rev.

Revs is just surface speed, with carbide 50m/min in stainless, 100m/min in steel, 200-500 m/min in aluminium or copper if you can clear the chips well
and/or coolant.

These rule-of-thumb numbers come from using HSMAdvisor and will get you in the ball park straight away.

Chiploads of 0.1 to 0.18 sounds awfully big chips. What units are you using?

Craig

My wife left with my best friend...
     and I miss him!

Offline RICH

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Re: RPM / Feed Rates Again?
« Reply #3 on: March 13, 2017, 08:58:15 AM »
Depth of cut must be taken into account when calculating a feed rate to be used. You are just considering one part of numerous influences pertaining to the cutting of a material.

stress= force x area ......
Still the basic formula but needs additonal factors applied to it to get meaningfull information for pratcical use.

A lot of research work was done over the years ago by professional societies and in particular by Cleveland. Metalic material properties are rather consistant and factors for horsepower,shear,etc have been developed through research for arriving at suggested feedrates etc. Wood and manny other materials require different factors to be applied as compared to metal. Manufactures information is sometimes available and for a particular material one needs to consult with them .

That said....................

You can calculate a lot of info from some basic calc's but any engineering calc is just a resonable guideline for consideration. Most of the calculators you find by the major tool manufactures are still based on research done years ago by the Society of Manufacturing Engineers and others. Other calculators provide all kinds of info, BUT, again it is just a consideration to be used in practical application.

FWIW,

RICH  

Offline kolias

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Re: RPM / Feed Rates Again?
« Reply #4 on: March 13, 2017, 10:25:04 AM »
......Chiploads of 0.1 to 0.18 sounds awfully big chips. What units are you using?
Craig

Yes the 0.1-0.18 is high because its in mm. Converting to inches now looks more reasonable

Thank you all for the help
Nicolas